Experimental evaluation of energy and exergy efficiency of a seasonal latent heat storage system for greenhouse heating

In the following work, a seasonal thermal energy storage using paraffin wax as a PCM with the latent heat storage technique was attempted to heat the greenhouse of 180 m² floor area. The system consists mainly of five units: (1) flat plate solar air collectors (as heat collection unit), (2) latent heat storage (LHS) unit, (3) experimental greenhouse, (4) heat transfer unit and (5) data acquisition unit. The external heat collection unit consisted of 27 m² of south facing solar air heaters mounted at a 55° tilt angle. The diameter and the total volume of the steel tank used as the latent heat storage unit were 1.7 m and 11.6 m³, respectively. The LHS unit was filled with 6000 kg of paraffin, equivalent to 33.33 kg of PCM per square meter of the greenhouse ground surface area. Energy and exergy analyses were applied in order to evaluate the system efficiency. The rate of heat transferred in the LHS unit ranged from 1.22 to 2.63 kW, whereas the rate of heat stored in the LHS unit was in the range of 0.65–2.1 kW. The average daily rate of thermal exergy transferred and stored in the LHS unit were 111.2 W and 79.9 W, respectively. During the experimental period, it was found that the average net energy and exergy efficiencies were 40.4% and 4.2%, respectively. The effect of the temperature difference of the heat transfer fluid at the inlet and outlet of the LHS unit on the computed values of the energy and exergy efficiency is evaluated during the charging period.     

高效利用低温水热量

通过分析低温水系统运行现状及存在的问题,提出确定甜机投运与停运条件、提高1#低温水温度、改造换热流程及增加热水换热负荷等优化运行方案。     

低温试验系统中露点温度控制的节能技术

通过对低温系统露点温度控制技术的分析,指出该控制模式存在的不足,提出采用露点模式和时间程序模式相结合的露点节能控制模式,对空气的干燥度和使用工况进行监控,从而实现对低湿度干燥空气的露点温度的智能监控。经比较,露点节能控制模式明显优于单纯的时间程序控制模式。     

High temperature solar heated seasonal storage system for low temperature heating of buildings

A preliminary study of a solar-heated low-temperature space-heating system with seasonal storage in the ground has been performed. The system performance has been evaluated using the simulation models TRNSYS and MINSUN together with the ground storage module DST. The study implies an economically feasible design for a total annual heat demand of about 2500 MWh. The main objective was to perform a study on Anneberg, a planned residential area of 90 single-family houses with 1080 MWh total heat demand. The suggested heating system with a solar fraction of 60% includes 3000 m² of solar collectors but electrical heaters to produce peak heating. The floor heating system was designed for 30°C supply temperature. The temperature of the seasonal storage unit, a borehole array in crystalline rock of 60,000 m³, varies between 30 and 45°C over the year. The total annual heating costs, which include all costs (including capital, energy, maintenance etc.) associated with the heating system, were investigated for three different systems: solar heating (1000 SEK MWh⁻¹), small-scale district heating (1100 SEK MWh⁻¹) and individual ground-coupled heat pumps (920 SEK MWh⁻¹). The heat loss from the Anneberg storage system was 42% of the collected solar energy. This heat loss would be reduced in a larger storage system, so a case where the size of the proposed solar heating system was enlarged by a factor of three was also investigated. The total annual cost of the solar heating system was reduced by about 20% to about 800 SEK MWh⁻¹, which is lower than the best conventional alternative.     

恒温阀作用下的低温地板辐射供暖系统室温动态变化仿真

为了研究恒温阀作用于低温地板辐射供暖系统时室内温度的动态响应,从恒温阀的室温控制原理出发,对房间、辐射地板、外围护结构的动态传热过程进行了分析,建立了动态传热的数学模型。依据数学模型搭建了低温地板辐射供暖系统室温动态控制的Simulink仿真模型,并对不同工况和不同室温设定模式下的室内温度和流量变化规律进行动态仿真,得到了不同模式下室内温度的变化曲线。     

地热-高温水源热泵供热系统的分析

运用能量系统的为(火用)分析方法.建立地热-高温水源热泵供热系统的炯分析理论模型.以实际工程项目为例,分析和讨论了系统运行条件下的能量有效利用,并计算了地热-高温热泵供热系统的火甩效率和各部分(火用)损失、(火用)效率.从计算结果看出,板式换热器的火用损失所占比例较大.     

建筑物供暖空调系统节能控制仿真

为了解决暖通空调控制系统的时滞、时变等非线性特征使其控制效果变差的问题,设计了在线辨识对象模型和基于SMITH预估器的自校正控制算法。实现了在线闭环辨识暖通空调特性参数,在获得相应模型后以SMITH预估器补偿时滞参数从而抵消各种消极状况,优化PI控制器加强其鲁棒性能。仿真结果表明所设计的在线辨识模型和控制算法取得了良好的控制效果并具备可行性。     

Optimisation of a Swedish district heating system with reduced heat demand due to energy efficiency measures in residential buildings

The development towards more energy efficient buildings, as well as the expansion of district heating (DH) networks, is generally considered to reduce environmental impact. But the combined effect of these two progressions is more controversial. A reduced heat demand (HD) due to higher energy efficiency in buildings might hamper co-production of electricity and DH. In Sweden, co-produced electricity is normally considered to displace electricity from less efficient European condensing power plants. In this study, a potential HD reduction due to energy efficiency measures in the existing building stock in the Swedish city Linköping is calculated. The impact of HD reduction on heat and electricity production in the Linköping DH system is investigated by using the energy system optimisation model MODEST. Energy efficiency measures in buildings reduce seasonal HD variations. Model results show that HD reductions primarily decrease heat-only production. The electricity-to-heat output ratio for the system is increased for HD reductions up to 30%. Local and global CO₂ emissions are reduced. If co-produced electricity replaces electricity from coal-fired condensing power plants, a 20% HD reduction is optimal for decreasing global CO₂ emissions in the analysed DH system.     

Optimal control of flow in low temperature solar heat collector

Solar energy collection plants with uniform flat plate collectors are classified according to the mode of operation and the type of performance criterion. The problem of optimal control of flow through the collector is formulated under simplifying assumptions and conditions for the existence of an optimal control of the system are stated for certain elements of the above classification. A numerical process for the optimal solution is described and an example of solution given. A simple control policy is given, applicable to those elements of the above classification where a continuous solution of the problem does not exist. This policy consists of alternate switching between zero and maximum available flow. A direction for further research into some aspects of the optimal control problem is suggested.     

相变储能太阳能热泵系统的试验研究

文章建立了相变储能太阳能热泵系统试验平台,介绍了系统的运行方式以及各个部分的运行原理,选取典型日进行试验,并对试验数据进行分析。分析结果表明:相变储能太阳能热泵系统能够满足北方农村的供暖需求,可以保证白天室内的温度达到22℃,COP的最大值为6.3;太阳能热泵系统停止工作后,相变储能箱可以保证室内温度达到供暖的需求温度7 h,起到了"削峰填谷"的作用,运行费用显著降低;相变储能太阳能热泵系统解决了单纯电加热供暖方式费用高、能耗高的问题,具有显著的节能性。     

A control strategy for energy optimal operation of a direct district heating system

A dynamic model of a direct district heating system (DDHS) is developed, and an energy optimal control strategy is designed. The DDHS is characterized as a system with long transport time delay. The use of a Smith predictor (SP) to deal with this type of time delay is explored. An SP is designed by using the reduced‐order dynamic model and implemented on the full‐order model. Also, optimal set point profiles of supply water temperature as a function of outdoor air temperature have been determined. The simulation results show that the SP works effectively in disturbance rejection compared with the nominal control design. The use of optimal set point control strategy resulted in energy savings of the order of 19–32% when the influence of internal load was considered. Copyright © 2004 John Wiley & Sons, Ltd.     

Experimental analysis of model predictive control for an energy efficient building heating system

Low energy buildings have attracted lots of attention in recent years. Most of the research is focused on the building construction or alternative energy sources. In contrary, this paper presents a general methodology of minimizing energy consumption using current energy sources and minimal retrofitting, but instead making use of advanced control techniques. We focus on the analysis of energy savings that can be achieved in a building heating system by applying model predictive control (MPC) and using weather predictions. The basic formulation of MPC is described with emphasis on the building control application and tested in a two months experiment performed on a real building in Prague, Czech Republic.     

考虑供热系统热储能特性的电-热综合系统随机优化调度模型研究

热电联产机组、热泵等装置的应用促进了电-热综合系统间的耦合关系,为风电的消纳提供了新途径。文章考虑了供热系统热储能动态特性,采用多场景法模拟风电出力不确定性,搭建了电-热综合能源系统随机优化调度模型。首先,针对供热管道传输时延动态特性,研究分析了其储热能力;其次,以电-热综合能源系统购能费用最低为目标函数,以热网约束、电网约束为约束条件,提出了综合系统能量最优化调度方案;最后,在IEEE33节点和6节点热网上进行算例分析,验证了模型的有效性。     

Experimental investigation of a calcium chloride-water heat storage system for off-peak energy supply and solar heating

One of the main difficulties in applying heat storage systems utilising the latent heat of calcium chloride hexahydrate is the incongruent character of the melting of the hexahydrate. The heat storage capacity of the system is considerably diminished by the separation of α-CaCl₂.4H₂O, forming a new phase. In externally non-mixed systems the separation of the tetrahydrate is practically irreversible and this causes the rapid deterioration of the heat storage system. During the experiments described in this paper the effects of the change in composition of the CaCl₂, 6H₂O heat storage material, of the impurities (NaCl, KCl, MgCl₂) and of thermoconvective flow on the formation of α-CaCl₂.4H₂O were investigated in externally non-mixed systems. It has been established that with a heat storage packing of more dilute (CaCl₂.6·3H₂O) total composition than the peritectic composition, favourable storage properties can be attained. To achieve this, the solid impurities have to be removed from the molten phase and the electric cable providing the heat input must be arranged to provide for adequate concentration equalisation by the convective thermal flow.     

Achievements and suggestions of heat metering and energy efficiency retrofit for existing residential buildings in northern heating regions of China

In order to promote energy efficiency and emission reduction, the importance of improving building energy efficiency received sufficient attention from Chinese Government. The heat metering and energy efficiency retrofit for existing residential buildings of 0.15 billion m² in northern heating regions of China was initiated in 2007 and completed successfully at the end of 2010. This article introduced the background and outline of the retrofit project during the period of 11th five-year plan. Numerous achievements that received by retrofit such as environmental protection effect, improvement of indoor environment, improvement of heating system, investment guidance effect, promotion of relevant industries and increasing chances of employment were concluded. Valuable experience that acquired from the retrofit project during the period of 11th five-year plan was also summarized in this article. By analyzing the main problems emerged in the past, pertinent suggestions were put forward to promote a larger scale and more efficient retrofit project in the period of 12th five-year plan.     

武汉地源热泵制热工况能效测评与效益分析

在武汉市地源热泵系统采暖季节测试的基础上,讨论了采暖工况下地源热泵机组及系统能效系数以及水系统输送系数,并与常规冷水机组+燃煤锅炉系统比较,分析了系统节能量、环境效益及增量投资回收期。得出结论:土壤源热泵水系统平均输送系数大于地下水源热泵系统;采暖工况地源热泵系统能效系数高于制冷工况,采暖季节比制冷季节节能率约高19.74%;单位建筑面积平均每年可减排二氧化碳18.35 kg、二氧化硫0.15 kg和粉尘0.074 3 kg;土壤源热泵系统的投资增量回收期比水源热泵系统高23%,费效比高32%。     

Hybrid photovoltaic-thermosyphon water heating system for residential application

In order to improve the energy performance of the photovoltaic system, much effort has been spent on the research and development of hybrid PVT (photovoltaic-thermal) technology using water as the coolant. The fin performance of the thermal absorber is known to be one crucial factor in achieving a high overall energy yield of the collector. Accordingly, an aluminum-alloy flat-box type PVT collector was constructed, with its fin efficiency approaching unity. Its design is primarily for natural circulation and for domestic water heating purpose. Our test results showed that a high final hot water temperature in the collector system can be achieved after a one-day exposure. A numerical model of this photovoltaic-thermosyphon collector system was also developed and the model accuracy was verified by comparison with measured data. The energy performance of the collector system was then examined first, through reduced-temperature analysis, and second, as applying in the “hot summer and cold winter” climate zone of China. The numerical results are found very encouraging, and the equipment is capable of extending the PV application potential in the domestic sector.     

供热计费方式与运行调节策略

阐述了收费体制改革前后热网运行调节思想的不同点 ,分析了不同收费体制下间连式热网的运行调节策略 ,研究了与室内采暖系统相适应的室外供热管网水系统变水量运行策略。     

太阳热水器与空气源热泵辅助加热集中供热水系统的工程设计

结合实例论述宾馆用太阳热水器与空气源热泵辅助集中供洗浴热水系统的工程设计方法,并着重介绍了空气源热泵的配置、布局、安装和控制.     

基于WebAccess的地源热泵远程能效测评系统的设计与实现

介绍了网际组态软件WebAccess的基本功能和地源热泵能效测评的主要内容,提出了基于WebAccess构建的地源热泵远程能效测评系统。阐述了系统总体设计方案,建立了以现场控制器ADAM-5510EKW/TP等为核心的监控节点硬件架构,并采用Muhiprog设计了现场控制器软件;完成了工程节点的系统工作界面设计,实现了地源热泵远程能效测评系统的各项功能。